Sclerotinia rot of carrot, caused by 'Sclerotinia sclerotiorum ' (Lib.) de Bary, occurs both pre- and post-harvest. The sporadic nature of disease and lack of correlation between disease incidence in the field and storage contribute to difficulties in disease control. Validation of a disease forecast model was conducted. Efficacy of spray regimes timed by the model and accuracy of the model in prediction of inoculum were tested. Disease thresholds were established and a validated model was produced for carrots grown in organic soil. To understand the link between disease in field and storage, the histopathology of disease progression from foliage to root was investigated. Disease progressed faster in storage than in actively-growing carrots. Two potential host resistance responses, abscission of infected tissue and formation of structural barriers near mycelium, were identified. Structural barriers may be involved in fungal latency. Disease management can be improved by utilizing the disease forecast model.